The bottom boundary layer of a fire whirl over a fuel pool is coupled to the outer rotating flow, the vaporization process, and the subsequent diffusional burning in the gas. As such, it plays an essential role in the dynamics of the fire whirl, particularly the resulting burning rate and flame height. In this paper, the bottom boundary-layer structure of a typical laminar fire whirl, generated by a rotating screen, is investigated both numerically and theoretically. The associated local similarity solutions of the momentum and coupling functions are derived, leading to the determination of the flame configuration as well as the surface gasification rate. It is demonstrated that the bottom boundary layer becomes thinner and the flame base is closer to the pool surface as the swirl intensity increases. As a result, the applied circulation increases the burning rate and thereby the flame height of the fire whirl by enhancing the convective heat transfer and the evaporation of the fuel, especially in the outer region of the fuel pool. The theoretical results agree well with the simulation results over a wide range of the Ekman number Ek and the Grashof number Gr, both qualitatively and quantitatively.

燃料池上方的火涡旋的底部边界层与外部旋转流，汽化过程以及随后的气体扩散燃烧耦合。因此，它在火涡旋的动力学中起着至关重要的作用，尤其是燃烧速度和火焰高度。在本文中，从数值和理论上研究了旋转筛产生的典型层流火旋涡的底部边界层结构。导出了动量和耦合函数的相关局部相似性解，从而确定了火焰构型以及表面气化速率。结果表明，随着旋流强度的增加，底部边界层变得更薄，火焰底部更靠近池表面。因此，所施加的循环通过增强对流传热和燃料的蒸发，特别是在燃料池的外部区域中，提高了燃烧速率，从而提高了火焰回旋的火焰高度。理论结果与广泛的Ekman数上的仿真结果非常吻合Ek和Grashof数Gr都在定性和定量上。